An existing wavelength division multiplexing (WDM) system usually uses a channel spacing of 50 GHz or 100 GHz, and all WDM paths usually use a same signal format and a same rate. That is, the existing wavelength division multiplexing system is a fixed-grid WDM system. As technologies such as super-speed, especially over 100 Gb/s, WDM transmission, networking, and a software defined network (SDN) develop, the conventional WDM system encounters challenges in terms of spectrum utilization, flexibility, scalability, and the like, and there is a need for application of a flexible-grid WDM system that supports different channel spacings and different transmission rates and that can dynamically set a channel spacing according to a requirement.
However, when a width of a flexible grid approximates a spectral width of a signal, filtering costs are extremely high. Currently, a method for resolving the problem is a super channel technology. In the super channel technology, transmission is performed on a same channel by using a plurality of adjacent subcarriers, and a guard band is added to an edge wavelength, to reduce the filtering costs. The channel is referred to as a super channel. However, due to a decrease in a wavelength spacing, a slight center wavelength offset causes relatively high system performance costs, and affects a link length. A center wavelength is a wavelength corresponding to a location with maximum power energy in a subcarrier.
It can be learned that how to precisely control a center wavelength of a subcarrier is an urgent technical problem that currently needs to be resolved.